[Ts mutants of the Eastern equine encephalomyelitis virus. Their generation, isolation and preliminary characterization]. / Ts-mutanty virusa vostochnogo éntsefalomielita loshadei. Poluchenie, vydelenie, predvaritel'naia kharakteristika.

Chick embryo fibroblast cultures of the C/O phenotype (leukemia--free) infected with eastern equine encephalomyelitis (EEE) virus were incubated in the presence of 15 micrograms/ml N-methyl-N-nitro-N-nitrosoguanidine in the culture medium. Seven (5%) temperature-sensitive mutants were isolated from cell homogenates only in those cases where cell cultures before infection had been treated with actinomycin D. The recovered ts mutants are characterized by the marked ts- phenotype and genetic stability. The method of obtaining EEE virus ts mutants under the effect of N-methyl-N-nitro-N-nitrosoguanidine in C/O phenotype (leukemia-free) chick embryo fibroblast cultures treated before virus inoculation with actinomycin D is discussed.

[Effect of the method of passage on the biological properties of attenuated alphavirus strains]. / Vliianie sposoba passirovaniia na biologicheskie svoistva attenuirovannykh shtammov al'favirusov.

Experiments with attenuated clones of Venezuelan equine encephalomyelitis virus and Eastern equine encephalomyelitis virus were carried out to study the regularities in changes of biological properties of virus in "undiluted" passages and in passages by subcultivation of small doses. In the latter case the biological activity of the virus remained at the initial low level but in "undiluted" passages it increased, due to accumulation in the population of clones with altered plaque phenotype and increased reproductive potential. In a number of cases this virus had a higher level of residual virulence than the original one. The evidence that the main source of virus variability in the "undiluted" passages lies, in genetic interaction in which defective virus takes part, is presented. Mixed infection with participation of defective interfering particles and the genetic interaction occurring in it are considered to be the mechanism which is conducive to restoration of biological activity of alphaviruses.

[Induction of alphavirus ts-mutations by N-methyl-N-nitro-N-nitrosoguanidine added to the replicating virus]. / Induktsiia ts-mutatsii al'favirusov N-metil-N-nitro-N-nitrozoguanidinom pri vozdeistvii na replitsiruiushchiisia virus.

The possibility of producing ts mutants of Sindbis and eastern equine encephalomyelitis (EEE) virus by treatment of replicating virus with N-methyl-N-nitro-N-nitrosoguanidine was studied. N-methyl-N-nitro-N-nitrosoguanidine added in a concentration of 20 micrograms/ml to chick fibroblast cultures infected with Sindbis virus for 4 hours was shown to induce ts mutations in the virus. Under similar conditions no ts mutants of EEE virus could be obtained. The content of ts mutants in the mutagenized populations of Sindbis virus was 7.9%. Eight ts mutants were isolated. Their temperature-sensitive defect was expressed to various degrees. The plaque-forming efficiency at 40 degrees C/35 degrees C ranged from 6.3 X 10(-2) to 1.7 X 10(-8), and the yield from 5.6 X 10(-2) to 2.8 X 10(-4).